According to an article in The Washington post, the hackers who attacked the Google China servers were looking for information about which Chinese intelligence operatives in the US were monitored by the US government.

When they initially announced the incident, Google claimed the attackers have accessed a database containing information related to intellectual property, so media outlets presumed the hackers were after source code and Google processes. However, according to former US officials, the Chinese were actually looking for a different type of intellectual property: court orders authorizing surveillance for Chinese agents using Gmail accounts.

“Knowing that you were subjects of an investigation allows them to take steps to destroy information, get people out of the country,” one anonymous former official told the Washington Post.

Washington Post reporter Ellen Nakashima also revealed that the hackers stumbled upon a database storing years' worth of information about US surveillance targets

“The most sensitive orders, however, came from a federal court that approves surveillance on foreign targets such as spies, diplomats, suspected terrorists, and agents of other governments. Those orders, issued under the Foreign Intelligence Surveillance Act, are classified,” she wrote.